Process chamber cleaning method in substrate processing apparatus, substrate processing apparatus, and substrate processing method

ABSTRACT

In a substrate processing apparatus configured to perform a predetermined process on a target substrate accommodated in a process chamber, the process chamber is cleaned by alternately performing an operation of generating plasma of a gas containing oxygen within the process chamber, and an operation of generating plasma of a gas containing nitrogen within the process chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/587,394filed Jul. 27, 2006, now U.S. Pat. No. 8,343,308 which is the nationalstage of International Patent Application No. PCT/JP2005/001057, filedJan. 27, 2005 and pursuant to 35. U.S.C., §119 claims the benefit ofpriority of Japanese Application No. 2004-020157, filed Jan. 28, 2004.The entire contents of U.S. Ser. No. 10/587,394 are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a process chamber cleaning method in asubstrate processing apparatus; a substrate processing apparatus; and asubstrate processing method, all of which are utilized in e.g., theprocess of manufacturing semiconductor devices.

BACKGROUND ART

For example, with an increase in miniaturization of the circuitstructures of semiconductor devices, substrate processing apparatusesused for manufacturing processes of semiconductor devices have beenrequired even more to set their process chambers for accommodatingsemiconductor substrates to have very high cleanliness.

Under the circumstances, for example, Patent Document 1 discloses atechnique in which a silicon crystal body is placed inside a processchamber at a region to face plasma. Contaminants are deposited on thesurface of the silicon crystal body and can be easily removed by acidsolution cleaning, thereby increasing the cleanliness of an area to beexposed to plasma within the process chamber.

Further, Patent Document 2 discloses a technique in which a cleaning gascomprising a nitrogen-containing compound and a fluorine-containingcompound is supplied into the process chamber of a deposition apparatusand plasma is generated. Consequently, residual substances presentwithin the process chamber are changed into volatile products andthereby removed.

Furthermore, Patent Document 3 discloses a technique in which a gas issupplied into a process chamber and turned into plasma. This plasma isused for performing sputter etching to remove contaminants from aceramic member disposed inside the process chamber.

However, according to the conventional techniques described above, ithas become difficult to meet cleanliness required in recent years,because of the following reasons. Specifically, the interior of aprocess chamber suffers corrosion of metal members due to corrosive gas,such as a fluorine-containing compound. Alternatively, the interior of aprocess chamber suffers damage of members disposed therein due tosputtering or re-deposition of sputtered contaminants.

For example, a step of forming gate oxide films in semiconductor devicesis important, because this step has a decisive influence on thecharacteristic of transistors. Since metal contaminants, such as iron(Fe) and copper (Cu), greatly and adversely affect the characteristic oftransistors, it is required to provide a decontamination technique thatcan attain higher cleanliness than the conventional technique.

On the other hand, as another process chamber cleaning method, theprocess chamber may be opened to the atmosphere and subjected to awiping treatment with purified water or solvent. However, where a highlevel of cleanliness is required, as described above, the cleanlinessmay rather be lowered and unsatisfactory due to contaminants carriedinto the process chamber opened to the atmosphere. Further, in order toset the process chamber opened to the atmosphere, it is necessary toperform operations of disassembling and reassembling the processchamber, which are troublesome and take a long time. This brings about atechnical problem such that the operation ratio of the substrateprocessing apparatus is significantly decreased.

-   [Patent Document 1] Jpn. Pat. Appln. KOKAI Publication No.    2002-353206-   [Patent Document 2] Jpn. Pat. Appln. KOKAI Publication No. 9-232299-   [Patent Document 3] Jpn. Pat. Appln. KOKAI Publication No. 11-3878

DISCLOSURE OF INVENTION

An object of the present invention is to provide a process chambercleaning method in a substrate processing apparatus, which can swiftlyclean the process chamber to be used for accommodating a targetsubstrate, without lowering the operation ratio of the substrateprocessing apparatus.

Another object of the present invention is to provide a process chambercleaning method in a substrate processing apparatus, which can clean theprocess chamber to be used for accommodating a target substraterelatively in a short time to a level necessary for a substrate processto be performed, even where the contamination degree inside the processchamber is relatively high, such as when a plasma processing apparatusis initially set up.

An alternative object of the present invention is to provide a processchamber cleaning method in a substrate processing apparatus, which doesnot cause corrosion of the interior of the process chamber due to acorrosive substance being used.

A further alternative object of the present invention is to provide aprocess chamber cleaning method in a substrate processing apparatus,which can clean the interior of the process chamber without causingcontamination due to sputtering or re-deposition of contaminants.

A further alternative object of the present invention is to provide asubstrate processing apparatus, which can be subjected to such processchamber cleaning, as described above.

A further alternative object of the present invention is to provide asubstrate processing method, which includes a step of process chambercleaning, as described above.

According to a first aspect of the present invention, there is provideda process chamber cleaning method in a substrate processing apparatusconfigured to perform a predetermined process on a target substrateaccommodated in a process chamber, the method comprising:

at least one cycle of alternately performing an operation of generatingplasma of a gas containing oxygen within the process chamber, and anoperation of generating plasma of a gas containing nitrogen within theprocess chamber.

According to a second aspect of the present invention, there is provideda computer readable storage medium containing software used for asubstrate processing apparatus configured to perform a predeterminedprocess on a target substrate accommodated in a process chamber, whereinthe software, when executed by a computer, controls the apparatus toclean the process chamber by alternately performing an operation ofgenerating plasma of a gas containing oxygen within the process chamber,and an operation of generating plasma of a gas containing nitrogenwithin the process chamber.

According to a third aspect of the present invention, there is provideda substrate processing apparatus comprising: a process chamberconfigured to accommodate a target substrate; a processing mechanismconfigured to perform a predetermined process on the target substratewithin the process chamber; a plasma generation mechanism configured togenerate plasma within the process chamber to clean an interior of theprocess chamber; and a control mechanism configured to control theplasma generation mechanism, wherein the control mechanism controls theplasma generation mechanism to clean the process chamber by at least onecycle of alternately performing an operation of generating plasma of agas containing oxygen within the process chamber, and an operation ofgenerating plasma of a gas containing nitrogen within the processchamber.

According to a fourth aspect of the present invention, there is provideda substrate processing method comprising: cleaning a process chamber byat least one cycle of alternately performing an operation of generatingplasma of a gas containing oxygen within the process chamber, and anoperation of generating plasma of a gas containing nitrogen within theprocess chamber; then, seasoning the process chamber by at least oneoperation of generating plasma of a gas containing oxygen or generatingplasma of a gas containing nitrogen within the process chamber; andthen, installing a target substrate into the process chamber andperforming a predetermined process on the target substrate.

According to the present invention, a process chamber cleaning processis executed by alternately generating oxygen plasma and nitrogen plasmawithin the process chamber in-situe, when a processing apparatus forperforming a predetermined process on a substrate, such as a processingapparatus for performing a plasma process, is initially set up, orbefore or after an objective process is performed. Consequently, it ispossible to reliably attain high cleanliness in a shorter time, ascompared with, e.g., a case where cleaning is performed only with singleplasma, such as oxygen plasma or nitrogen plasma, or a case wherecleaning is performed while setting a process chamber opened to theatmosphere.

As a result, the process chamber for accommodating a target substrate inthe substrate processing apparatus can be cleaned to an aimingcleanliness level, without lowering the operation ratio or throughput ofthe substrate processing apparatus.

Further, the process chamber for accommodating a target substrate can becleaned relatively in a short time to a level necessary for a substrateprocess to be performed, even where the contamination degree inside theprocess chamber is relatively high, such as when the plasma processingapparatus is initially set up.

Furthermore, since the plasma used consists of, e.g., oxygen plasma ornitrogen plasma, high cleanliness can be obtained without causingcorrosion of the interior of the process chamber due to a corrosivesubstance being used.

Furthermore, since the process chamber cleaning employs a plasma processwith low electron temperature plasma, the interior of the processchamber can be further cleaned without causing sputtering damage tomembers inside the process chamber, or contamination due to re-adhesionof contaminants derived from a contamination source generated by thesputtering.

In the present invention, the plasma used in the cleaning consistspreferably of low electron temperature plasma. The low electrontemperature plasma means plasma having an electron temperature of about0.5 to 3 eV. In this case, the low electron temperature plasma ispreferably set to have an electron temperature of 2 eV or less. Theelectron temperature to be used may be defined by a mean squarevelocity. The electron temperature is preferably set to be 2 eV or lessnear the chamber inner wall. The plasma is preferably generated bymicrowaves supplied into the process chamber through a planar antennahaving a plurality of slots. With this arrangement, it is possible torealize low electron temperature plasma, as desired.

The predetermined process performed in the processing apparatus ispreferably a process with low electron temperature plasma. This processis preferably a nitriding process or oxidizing process. Further, the gascontaining oxygen is preferably oxygen gas, and the gas containingnitrogen is preferably nitrogen gas.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view schematically showing an example of a plasmaprocessing apparatus to be subjected to a process chamber cleaningmethod according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of the structure of acontrol section used in the plasma processing apparatus according to theembodiment of the present invention.

FIG. 3 is a timing chart showing an example of a process chambercleaning method according to the embodiment of the present invention.

FIG. 4 is a timing chart showing another example of a process chambercleaning method according to the embodiment of the present invention.

FIG. 5 is a graph showing contamination degree obtained where a processchamber cleaning method according to the present invention was actuallyperformed.

FIG. 6 is a graph showing contamination degree obtained where a processchamber cleaning method according to the present invention was actuallyperformed.

FIG. 7 is a graph showing contamination degree obtained where processchamber cleaning was performed only with nitrogen plasma, forcomparison.

FIG. 8 is a graph showing contamination degree obtained where processchamber cleaning was performed only with nitrogen plasma, forcomparison.

FIG. 9A is a graph showing contamination degree obtained before andafter a cleaning process where a process chamber cleaning methodaccording to the present invention was actually performed with anitrogen plasma process set at a pressure of 126.7 Pa.

FIG. 9B is a graph showing contamination degree obtained before andafter a cleaning process where a process chamber cleaning methodaccording to the present invention was actually performed with anitrogen plasma process set at a pressure of 66.7 Pa.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 is a sectional view schematically showing an example of a plasmaprocessing apparatus to be subjected to a process chamber cleaningmethod according to an embodiment of the present invention. FIG. 2 is ablock diagram showing an example of the structure of a control sectionused in the plasma processing apparatus according to this embodiment.FIG. 3 is a timing chart showing an example of a process chambercleaning method according to this embodiment. FIG. 4 is a timing chartshowing another example of a process chamber cleaning method accordingto this embodiment.

This plasma processing apparatus 200 is arranged to perform a process,such as a nitriding process or oxidizing process, using microwaveplasma. The apparatus 200 includes a substantially cylindrical chamber71, which is airtight and grounded. The bottom wall 71 a of the chamber71 has a circular opening 80 formed at the center, and is provided withan exhaust chamber 81 communicating with the opening 80 and extendingdownward. The chamber 71 is provided with a susceptor 72 disposedtherein and made of a ceramic, such as AlN, for supporting a targetsubstrate, such as a wafer W or dummy wafer Wd, in a horizontal state.The susceptor 72 is supported by a cylindrical support member 73extending upward from the center of the bottom of the exhaust chamber81. The susceptor 72 is provided with a guide ring 74 disposed on theouter edge to guide the wafer W. The susceptor 72 is further providedwith a heater 75 of the resistance heating type embedded therein. Theheater 75 is supplied with a power from a heater power supply 76 to heatthe susceptor 72, thereby heating the target object or wafer W. Theheater power supply 76 is controlled by a process controller 301described later, with reference to signals of a thermocouple 77 used asa temperature sensor, to set the heater 75 at a predetermined output.

The susceptor 72 is provided with three wafer support pins 82 (only twoof them are shown) that can project and retreat relative to the surfaceof the susceptor 72 to support the wafer W and move it up and down. Thewafer support pins 82 are fixed to a support plate 83, and are moved upand down along with the support plate 83 by an elevating mechanism 84,such as an air cylinder.

A gas feed member 85 is disposed on the sidewall of the chamber 71, andis connected to a gas supply system 86. The gas supply system 86includes an N₂ gas supply source 87, an Ar gas supply source 88, and anO₂ gas supply source 89, from which gases are supplied throughrespective gas lines 90 to the gas feed member 85 and are respectivelydelivered from the gas feed member 85 into the chamber 71. Each of thegas lines 90 is provided with a mass-flow controller 91 and twoswitching valves 92 for opening closing each of the gas lines one oneither side of the controller 91.

The sidewall of the exhaust chamber 81 is connected to an exhaust unit94 including a high-speed vacuum pump through an exhaust line 93. Theexhaust unit 94 can be operated to uniformly exhaust the gas from insidethe chamber 71 into the space 81 a of the exhaust chamber 81, and thenout of the exhaust chamber 81 through the exhaust line 93. Consequently,the pressure inside the chamber 71 can be decreased at a high speed to apredetermined vacuum level.

The chamber 71 has a transfer port 95 formed in the sidewall andprovided with a gate valve 96 for opening/closing the transfer port 95.The wafer W or dummy wafer Wd is transferred between the plasmaprocessing apparatus 200 and an adjacent transfer chamber (not shown)through the transfer port 95. A reference symbol 71 b denotes a quartzliner.

The top of the chamber 71 has an opening and is provided with an annularsupport portion 97 projecting along the periphery of the opening. Amicrowave transmission plate 98 is airtightly disposed on the supportportion 97 through a seal member 99. The microwave transmission plate 98is made of a dielectric material, such as quartz or a ceramic, e.g.,AlN, to transmit microwaves. The interior of the chamber 71 is thus heldairtight.

A circular planar antenna member 101 is disposed above the microwavetransmission plate 98 to face the susceptor 72. The planar antennamember 101 is attached to the top of the sidewall of the chamber 71. Theplanar antenna member 101 is formed of, e.g., a copper plate or aluminumplate with the surface plated with silver or gold. The planar antennamember 101 has a plurality of microwave radiation holes 102 formed oflong groove slots or circular through-holes arrayed in a predeterminedpattern. A retardation member 103 having a high dielectric constantcharacteristic with a dielectric constant larger than that of vacuum isdisposed on the top of the planar antenna member 101. The planar antennamember 101 and retardation member 103 are covered with a shield cover104 disposed at the top of the chamber 71. A seal member 105 isinterposed between the top of the chamber 71 and the shield cover 104 toseal this portion. The shield cover 104 is provided with cooling waterpassages (not shown) formed therein to cool the shield cover 104 andretardation member 103 by a cooling water flowing therethrough. Theshield cover 104 is grounded. The planar antenna member 101 is separatedfrom the microwave transmission plate 98 in FIG. 1, but they may be incontact with each other.

The shield cover 104 has an opening 106 formed at the center of theupper wall and connected to a waveguide 107. The waveguide 107 isconnected to a microwave generation unit 109 at one end through amatching circuit 108. The microwave generation unit 109 generatesmicrowaves with a frequency of, e.g., 2.45 GHz, which are transmittedthrough the waveguide 107 to the planar antenna member 101. Themicrowaves may have a frequency of 8.35 GHz or 1.98 GHz.

The waveguide 107 includes a coaxial waveguide 107 a having a circularcross-section and extending upward from the opening 106 of the shieldcover 104, and a rectangular waveguide 107 b having a rectangularcross-section, connected to the upper end of the coaxial waveguide 107a, and extending in a horizontal direction. The rectangular waveguide107 b has a mode transducer 110 at the end connected to the coaxialwaveguide 107 a. The coaxial waveguide 107 a includes an innerconductive member 111 extending at the center, which is connected andfixed to the center of the planar antenna member 101 at the lower end.

The respective components of the plasma processing apparatus 200 areconnected to a control section 300. As shown in FIG. 2, the controlsection 300 comprises a process controller 301, a user interface 302,and a recipe database 303.

The process controller 301 is connected to respective components, suchas the heater power supply 76, elevating mechanism 84, mass-flowcontroller 91, switching valve 92, exhaust unit 94, gate valve 96,matching circuit 108, and microwave generation unit 109, so that theprocess controller 301 controls them. Further, the process controller301 is connected to a thermocouple 77 used as a temperature sensor, sothat the process controller 301 controls the heater power supply 76 withreference to signals of the thermocouple 77.

The user interface 302 includes, e.g., a keyboard and a display, whereinthe keyboard is used for a process operator to input commands foroperating the plasma processing apparatus 200, and the display is usedfor showing visualized images of the operational status of the plasmaprocessing apparatus 200.

The recipe database 303 stores control programs for the processcontroller 301 to control the plasma processing apparatus 200 so as toperform various processes, and programs or recipes for respectivecomponents of the plasma processing apparatus 200 to perform processesin accordance with process conditions. Recipes may be stored in a harddisk or semiconductor memory, or stored in a portable storage medium,such as a CDROM or DVD, to be attached to a predetermined position inthe recipe database 303. Further, recipes may be transmitted fromanother apparatus through, e.g., a dedicated line, as needed.

A required recipe is retrieved from the recipe database 303 and executedby the process controller 301 in accordance with an instruction or thelike through the user interface 302. Consequently, the plasma processingapparatus 200 can perform a predetermined process under the control ofthe process controller 301.

In this embodiment, the recipe database 303 stores a nitriding plasmaprocess recipe 303 b for performing a nitriding process on the surfaceof a wafer W, using plasma of nitrogen gas supplied from the N₂ gassupply source 87. The recipe database 303 also stores an oxidizingplasma process recipe 303 c for performing an oxidizing process on thesurface of a wafer W, using plasma of oxygen gas supplied from the O₂gas supply source 89. In addition, the recipe database 303 stores acleaning process recipe 303 a for performing process chamber cleaning asexemplified by the chart shown in FIG. 3.

This cleaning process recipe 303 a is arranged to perform a process suchthat oxygen plasma PO and nitrogen plasma PN are alternately generatedwithin the chamber 71 at least one cycle and independently of each otherin an arbitrary order. Specifically, a process of generating one of theoxygen plasma PO and nitrogen plasma PN is first performed, and aprocess of generating the other of them is then performed. Thisalternate cycle is performed only one time, or repeated a plurality oftimes. This cycle is preferably repeated a plurality of times, and morepreferably repeated three times or more. The cleaning process recipe 303a also includes, as needed, a seasoning process in which an oxygenplasma process or nitrogen plasma process is performed one time orrepeated a plurality of times.

In this case, the oxygen plasma PO employs the following conditions.Specifically, the oxygen plasma generation period TO is set to be, e.g.,10 seconds to 3 minutes, and preferably 30 seconds to 100 seconds. Theflow rate of O₂ gas is set to be 0.005 to 5.0 L/minute. The flow rate ofAr gas used as a carrier gas is set to be 0.1 to 5.0 L/minute. Thepressure inside the chamber 71 is set to be 6 to 633 Pa.

On the other hand, the nitrogen plasma PN employs the followingconditions. Specifically, the nitrogen plasma generation period TN isset to be, e.g., 10 seconds to 3 minutes, and preferably 30 seconds to100 seconds. The flow rate of N₂ gas is set to be 0.05 to 1.0 L/minute.The flow rate of Ar gas used as a carrier gas is set to be 0.1 to 3.0L/minute. The pressure inside the chamber 71 is set to be 60 to 150 Pa.

The cycle-middle recess period Ti between the oxygen plasma generationperiod TO and nitrogen plasma generation period TN is set to be, e.g.,20 to 40 seconds. The cycle-end recess period Tj at the end of eachcycle is set to be, e.g., 20 to 40 seconds.

According to the cleaning process recipe 303 a, one cycle is defined bya period from the oxygen plasma generation period TO to the cycle-endrecess period Tj. For example, this cycle is repeated until the chamber71 reaches an aiming cleanliness level.

The radio frequency power supplied from the microwave generation unit109 to the chamber 71 is preferably set to be 500 W to 5 kW. The radiofrequency power has a frequency of 2.45 GHz.

In the cleaning process, where the plasma potential of the oxygen plasmaPO or nitrogen plasma PN is increased, the flow rate of oxygen gas ornitrogen gas is decreased. Where the electron temperature of the plasmais decreased, the flow rate of oxygen gas or nitrogen gas is increased.

The carrier gas used when the oxygen plasma PO or nitrogen plasma PN isgenerated is not limited to Ar, and it may be another inactive gas, suchas Kr. The electron temperature of the plasma can be changed, dependingon the carrier gas.

Next, an explanation will be given of a process operation performed inthe plasma processing apparatus 200.

At first, a nitriding process will be explained as an example of aprocess performed in the plasma processing apparatus 200. Specifically,the gate valve 96 is opened, and a clean wafer W is loaded through thetransfer port 95 into the chamber 71 and placed on the susceptor 72.

Then, N₂ gas and Ar gas are supplied at predetermined flow rates fromthe N₂ gas supply source 87 and Ar gas supply source 88 of the gassupply system 86 through the gas feed member 85 into the chamber 71,while the chamber 71 is maintained at a predetermined pressure.

At this time, microwaves are supplied from the microwave generation unit109 through the matching circuit 108 into the waveguide 107. Themicrowaves are supplied through the rectangular waveguide 107 b, modetransducer 110, and coaxial waveguide 107 a in this order to the planarantenna member 101. Then, the microwaves are radiated from the planarantenna member 101 through the microwave transmission plate 98 into thespace above the wafer W within the chamber 71. In this case, thewavelength of the microwaves has been shortened by the retardationmember 103. The microwaves are propagated in a TE mode through therectangular waveguide 107 b. The microwaves are converted from the TEmode into a TEM mode by the mode transducer 110. The microwaves in theTEM mode are propagated through the coaxial waveguide 107 a toward theplanar antenna member 101.

When the microwaves are radiated from the planar antenna member 101through the microwave transmission plate 98 into the chamber 71, N₂ gasand Ar gas being supplied are turned into plasma within the chamber 71by the microwaves. With the nitrogen plasma thus generated, a nitridingprocess is performed on the surface of the wafer W.

The microwave plasma thus generated has a high plasma density and a lowelectron temperature. A process using such low electron temperatureplasma has merits such that the underlayer can suffer less damage and soforth, and thus is suitably applied to a plasma process around gates.The low electron temperature plasma means plasma having an electrontemperature of about 0.5 to 3 eV. In order to effectively exercisemerits, such as small damage to the underlayer and so forth, theelectron temperature is preferably set to be 2 eV or less. As describedabove, the microwave plasma can be controlled by adjusting conditionsfor generation to set the electron temperature to be 2 eV or less, or tobe still lower with 1 eV or less. The electron temperature to be usedmay be defined by a mean square velocity. The electron temperature ispreferably set to be 2 eV or less near the chamber inner wall.

In the plasma processing apparatus 200, an oxidizing process usingoxygen plasma can be also performed on the surface of a wafer W. In thiscase, in place of N₂ gas, O₂ gas is supplied from the O₂ gas supplysource 89 along with Ar gas into the chamber 71, so that a process usingmicrowave plasma is similarly performed.

Where a process using such microwave plasma is performed, the acceptablelevel of contamination due to metal elements or the like within thechamber 71 is very low, and, e.g., the number of contaminant atoms hasto be 2×2¹⁰/cm² or less. If the contamination is higher, thecharacteristics of semiconductor devices are damaged and the yieldthereof is lowered. Accordingly, very high cleanliness is required.

According to this embodiment, in order to realize such very highcleanliness, process chamber cleaning is performed, as follows.

For example, it may be necessary to remove contamination within thechamber 71, when the plasma processing apparatus 200 is initially setup, or before and after a nitriding plasma process or oxidizing plasmaprocess is performed on each lot of wafers W. In such a case, as needed,an instruction can be input through the user interface 302 into theprocess controller 301 to retrieve and execute the cleaning processrecipe 303 a. Alternatively, a part of another recipe may be arranged toautomatically retrieve and execute the cleaning process recipe 303 aaccording to this embodiment.

When the cleaning process recipe 303 a is executed in the plasmaprocessing apparatus 200, the gate valve 96 is opened, and a clean dummywafer Wd is loaded through the transfer port 95 into the chamber 71 andplaced on the susceptor 72. This operation is performed to protect thesusceptor 72 from oxygen plasma PO or nitrogen plasma PN by the dummywafer Wd. Since this embodiment uses plasma with a low electrontemperature, the dummy wafer Wd does not necessarily have to be placedon the susceptor 72.

Then, the cleaning process shown in FIG. 3 or 4 is started. At first,while the interior of the chamber 71 is maintained at a predeterminedpressure of, e.g., 10 to 300 Pa, O₂ gas and Ar gas are supplied at flowrates of 5 to 1,000 mL/min and 0.1 to 3 L/min, respectively, from the O₂gas supply source 89 and Ar gas supply source 88 of the gas supplysystem 86 through the gas feed member 85 into the chamber 71.

At this time, microwaves are supplied from the microwave generation unit109 through the matching circuit 108 into the waveguide 107, as in themain plasma processes, such as the nitriding process described above.The microwaves are supplied through the rectangular waveguide 107 b,mode transducer 110, and coaxial waveguide 107 a in this order to theplanar antenna member 101. Then, the microwaves are radiated from theplanar antenna member 101 through the microwave transmission plate 98into the space above the dummy wafer W within the chamber 71.

When the microwaves are radiated from the planar antenna member 101through the microwave transmission plate 98 into the chamber 71, O₂ gasand Ar gas are turned into plasma within the chamber 71 by themicrowaves, and oxygen plasma PO is thereby generated. With the oxygenplasma PO thus generated, cleaning of the interior of the chamber 71 isperformed for an oxygen plasma generation period TO, using O radicals(O*) and so forth contained in the oxygen plasma PO. The microwaveplasma thus generated is low electron temperature plasma having anelectron temperature of 2 eV or less, or a still lower electrontemperature of 1 eV or less, as described above.

Then, supply of O₂ gas and application of radio frequency power from themicrowave generation unit 109 are stopped, so that the plasma is stoppedfor a cycle-middle recess period Ti. During this cycle-middle recessperiod Ti, supply of Ar used as a carrier gas is continued, so that theinterior of the chamber 71 is maintained at a predetermined pressure.

Then, N₂ gas is supplied at a flow rate of 5 to 1,000 mL/min from the N₂gas supply source 87 of the gas supply system 86 through the gas feedmember 85 into the chamber 71. Further, application of the radiofrequency power from the microwave generation unit 109 is restarted.When the microwaves are radiated from the planar antenna member 101through the microwave transmission plate 98 into the chamber 71, N₂ gasand Ar gas are turned into plasma within the chamber 71 by themicrowaves, and nitrogen plasma PN is thereby generated. With thenitrogen plasma PN thus generated, cleaning of the interior of thechamber 71 is performed for a nitrogen plasma generation period TN,using N radicals (N*) and so forth contained in the nitrogen plasma PN.The pressure inside the chamber during this nitrogen plasma step has aninfluence on the contamination degree. In order to lower thecontamination degree, the pressure inside the chamber is preferably setto be 133.3 Pa or less, and more preferably to be 13.3 to 93.3 Pa, andfurthermore preferably to be 26.6 to 66.7 Pa.

When the nitrogen plasma generation period TN has elapsed, supply of N₂gas into the chamber 71 and application of radio frequency power fromthe microwave generation unit 109 are stopped for a cycle-end recessperiod Tj.

The cycle described above is repeated the necessary number of times tocomplete cleaning inside the chamber 71. Then, the dummy wafer Wd isunloaded from the chamber 71.

As described above, this cleaning process is performed without settingthe chamber 71 opened to the atmosphere, and thus the operation ratio orthroughput of the plasma processing apparatus 200 is prevented frombeing impaired. The cleaning process can be performed only by retrievingand executing the cleaning process recipe 303 a, so that contaminantsinside the chamber is removed relatively in a short time to attain veryhigh cleanliness. Consequently, the productivity of the plasma processstep is improved.

For example, when the plasma processing apparatus 200 is initially setup, the contamination degree inside the process chamber is relativelyhigh. Further, there may be a case where a wafer W with a highcontamination degree is accidentally loaded into the chamber 71. Even insuch cases, the chamber 71 can be cleaned relatively in a short time toa high level necessary for a plasma process to be performed.Consequently, the yield of semiconductor devices to be formed on wafersW is improved.

Further, the cleaning process does not employ a corrosive substance,such as a fluorine compound, so the interior of the process chamber isprevented from being corroded. In addition, the cleaning process employslow electron temperature plasma, as described above, so the interior ofthe process chamber is prevented from suffering contamination due tosputtering or re-adhesion of contaminants. Consequently, the processchamber can be cleaned to a high level.

In this embodiment, the last cycle for performing process chambercleaning includes a final process period TF using nitrogen plasma PN oroxygen plasma PO generated at the end, which is longer, e.g., threetimes or more longer, than the former nitrogen plasma generation periodTN or oxygen plasma generation period TO. This arrangement makes itpossible to reliably prevent a subsequent process, to be performed afterthe process chamber cleaning, from being affected by the oxygen plasmaPO or nitrogen plasma PN alternately generated within the chamber 71during the process chamber cleaning.

Further, in this embodiment, the plasma processing apparatus 200 canperform, as a primary plasma process function, either one of a nitridingprocess on a wafer W while supplying N₂ gas and Ar gas into the chamber71, and an oxidizing process on a wafer W while supplying O₂ gas and Argas into the chamber 71. Accordingly, the process chamber cleaningdescribed above can be executed before either of the nitriding processand oxidizing process is performed on a wafer W. At this time, the typeof plasma generated within the chamber 71 subsequently to the processchamber cleaning is preferably set to agree with that used in thesubsequent plasma process performed on a wafer W, i.e., depending onwhether the subsequent process is the nitriding process or oxidizingprocess.

Specifically, the process chamber cleaning may be executed before thenitriding process is performed on a wafer W while supplying N₂ gas andAr gas into the chamber 71. In this case, as shown in FIG. 3, after theprocess chamber cleaning, a final process period TF including nitrogenplasma generation and vacuum-exhaust is performed at least one cycle toexecute a seasoning process. Then, the nitriding process is performed onthe wafer W.

Alternatively, the process chamber cleaning may be executed before theoxidizing process is performed on a wafer W while supplying O₂ gas andAr gas. In this case, as shown in FIG. 4, after the process chambercleaning, a process period TF including oxygen plasma generation andvacuum-exhaust is performed at least one cycle to execute a seasoningprocess. Then, the oxidizing process is performed on the wafer W.

Consequently, the preceding process chamber cleaning is prevented fromaffecting the subsequent actual process on a wafer W. However, suchagreement is not necessary required in some cases.

Next, an explanation will be given of a specific instance of asequential flow of the cleaning process, seasoning process, andnitriding process. In the following explanation, numerical values aremere examples and not limiting.

At first, after a predetermined process, such as a nitriding process, isperformed, Ar gas and O₂ gas are supplied at flow rates of 1 L/min and0.2 L/min, respectively, into the chamber, while the pressure in thechamber is set at, e.g., 126.7 Pa. Further, the susceptor is heated toset the wafer temperature (susceptor temperature) at 400°, so as toperform pre-heating for 30 seconds. Then, while the pressure and theflow rates of Ar gas and O₂ gas are maintained, microwaves are suppliedat 2,000 W to ignite oxygen plasma in a high-pressure state thatfacilitates the ignition. Then, the process pressure is set at 66.7 Pa,and oxygen plasma PO is generated for 60 seconds. After this oxygenplasma process step is finished, the plasma is turned off, and,subsequently thereto, Ar gas and O₂ gas are stopped and vacuum-exhaustis performed for 30 seconds.

Then, Ar gas and N₂ gas are supplied at flow rates of 1 L/min and 0.15L/min, respectively, into the chamber, while the pressure in the chamberis set at, e.g., 126.7 Pa. Further, the susceptor is heated to set thewafer temperature (susceptor temperature) at 400°, so as to performpre-heating for 30 seconds. Then, while the pressure and the flow ratesof Ar gas and N₂ gas are maintained, microwaves are supplied at 1,600 Wto ignite nitrogen plasma. Then, the process pressure is set at 66.7 Pa,and nitrogen plasma PN is generated for 60 seconds. After this nitrogenplasma process step is finished, the plasma is turned off, and,subsequently thereto, Ar gas and N₂ gas are stopped and vacuum-exhaustis performed for 30 seconds.

The cycle described above is performed at least one cycle to completethe cleaning process.

After the last plasma process step is finished and vacuum-exhaust isperformed for 30 seconds, the seasoning process is executed. Where theseasoning process is followed by a nitriding process, the seasoningprocess is executed as follows. Specifically, Ar gas and N₂ gas aresupplied at flow rates of 1 L/min and 0.15 L/min, respectively, into thechamber, while the pressure in the chamber is set at, e.g., 126.7 Pa.Further, the susceptor is heated to set the wafer temperature (susceptortemperature) at 400°, so as to perform pre-heating for 30 seconds. Then,while the pressure and the flow rates of Ar gas and N₂ gas aremaintained, microwaves are supplied at 1,600 W to ignite nitrogenplasma. Then, the process pressure is set at 66.7 Pa, and nitrogenplasma PN is generated for 180 seconds. After this nitrogen plasmaprocess step is finished, the plasma is turned off, and, subsequentlythereto, Ar gas and N₂ gas are stopped and vacuum-exhaust is performed.This cycle is performed a predetermined number of times to complete theseasoning, and then the nitriding process is executed as a primaryprocess.

Next, an explanation will be given of results obtained where thecleaning process described above was actually performed.

FIGS. 5 and 6 show effects obtained where the cleaning process accordingto this embodiment was performed. In these drawings, the horizontal axisdenotes cumulative time in the process chamber cleaning process, and thevertical axis denotes contamination degree on the surface of examinationsamples (the number of contaminant atoms per unit area). FIG. 5 showsresults obtained by the cleaning process performed after the oxidizingprocess using oxygen plasma. FIG. 6 shows results obtained by thecleaning process performed after the nitriding process using nitrogenplasma.

In these experiments, the chamber was first forcibly contaminated, and aclean sample wafer was placed in the chamber. Then, the oxidizingprocess and nitriding process was respectively performed underpredetermined conditions to prepare a contamination examination samplefrom the sample wafer. The examination sample thus prepared was examinedby ICP-MASS (Inductive Coupled Plasma Mass Spectrometry) to measure thenumber of contaminant atoms per unit area (corresponding to 0 (min) inFIGS. 5 and 6).

Next, a clean sample wafer was placed in the chamber, and a cyclecomprising a step of using oxygen plasma PO for one minute and a step ofusing nitrogen plasma PN for one minute was repeated 15 times, i.e., acleaning operation was performed for 30 minutes in total, to prepare anexamination sample from the sample wafer. The examination sample thusprepared was examined by ICP-MASS to measure the number of contaminantatoms per unit area (corresponding to 30 (min) in FIGS. 5 and 6). Next,this operation was further repeated four times, i.e., the number oftimes in repeating the operation was five in total, to prepare anexamination sample from the sample wafer at each time the cleaningoperation was finished. The examination sample thus prepared wasexamined by ICP-MASS to measure the number of contaminant atoms per unitarea (corresponding to 60, 90, 120, and 150 (min) in FIGS. 5 and 6). Inthis case, Cu, Fe, K, Al, Mg, and Na were measured as contaminants.

Specific conditions used in the cleaning process were as follows:

(1) Oxygen plasma step (per unit step):

Wafer temperature (susceptor temperature): 400°,

Pressure: 66.7 Pa,

O₂ gas flow rate: 0.2 L/min,

Ar gas flow rate: 1 L/min,

Time: 30 sec, and

Microwave power: 2,000 W.

(2) Nitrogen plasma step (per unit step):

Wafer temperature (susceptor temperature): 400°,

Pressure: 66.7 Pa,

N₂ gas flow rate: 0.15 L/min,

Ar gas flow rate: 1 L/min,

Time: 60 sec, and

Microwave power: 1,600 W.

As shown in FIGS. 5 and 6, the cleanliness reached a desired value of2×10¹⁰ atoms/cm² or less in a very short time of 150 minutes, withoutsetting the chamber 71 opened to the atmosphere, by the cleaning processaccording to this embodiment performed after either one of the oxidizingprocess and nitriding process. Accordingly, it has been confirmed thatthe chamber 71 can be swiftly cleaned by the process chamber cleaning toa level necessary for a plasma process to be performed on a wafer W,which severely requires a lower contamination level in recent years.

For comparison, FIGS. 7 and 8 show results obtained where a cleaningprocess was performed only with nitrogen plasma PN. In these drawings,the horizontal axis denotes cumulative time in the process chambercleaning process, and the vertical axis denotes contamination degree onthe surface of examination samples (the number of contaminant atoms perunit area). FIG. 7 shows results obtained by the cleaning processperformed after the interior of the chamber was forcibly contaminatedand then the oxidizing process using oxygen plasma was performed. FIG. 8shows results obtained by the cleaning process performed after theinterior of the chamber was forcibly contaminated and then the nitridingprocess using nitrogen plasma was performed. Also in this case, Cu, Fe,K, Al, Mg, and Na were measured as contaminants.

In the comparative experiments, a cleaning operation for 30 minutes onlywith nitrogen plasma PN was repeated five times in total to prepare anexamination sample, as in FIGS. 5 and 6 described above. As a result, asshown in FIGS. 7 and 8, it was confirmed that, where a cleaning processwas performed by repeating nitrogen plasma PN alone, the cleanliness didnot reach a desired value of 2×10¹⁰ atoms/cm² or less in 150 minutes, ineither case after the oxidizing process was performed or the nitridingprocess was performed.

Next, experiments were conducted to perform a cleaning process withdifferent values of the pressure in the nitrogen plasma step. In theseexperiments, a nitriding process was performed under conditions setforth below. Then, when the cleaning process was performed, the pressurein the nitrogen plasma was set at different values of 126.7 Pa and 66.7Pa. Conditions used at this time were as follows:

(1) Nitriding process:

Pressure: 6.7 Pa,

N₂ gas flow rate: 40 mL/min,

Ar gas flow rate: 1 L/min,

Time: 20 sec, and

Microwave power: 1,500 W.

(2) Cleaning process:

(i) Oxygen plasma process (per unit step):

Pressure: 66.7 Pa,

O₂ gas flow rate: 0.2 L/min,

Ar gas flow rate: 1 L/min,

Time: 30 sec, and

Microwave power: 2,000 W.

(ii) Nitrogen plasma process (per unit step):

Pressure: 126.7 Pa or 66.7 Pa,

N₂ gas flow rate: 0.15 L/min,

Ar gas flow rate: 1 L/min,

Time: 60 sec, and

Microwave power: 1,600 W.

The cleaning process was performed by repeating the oxygen plasma stepand nitrogen plasma step described above 15 times. Before and after thecleaning process, a contamination examination sample was prepared fromthe sample wafer by nitriding process plasma. The examination samplethus prepared, before and after the cleaning process, was examined byICP-MASS to measure the contamination degree (the number of contaminantatoms per unit area) in terms of Na, Al, Fe, Cu, Cr, Ni, Mg, and Ca.FIGS. 9A and 9B show results of the experiments. As regards FIG. 9A, Crwas not higher than the detection limit both before and after thecleaning process. As regards FIG. 9B, Cr was not higher than thedetection limit before the cleaning process, and Na, Fe, Cu, Cr, Ni, andMg were not higher than the detection limit after the cleaning process.

As shown in FIGS. 9A and 9B, it was confirmed that the effect of thecleaning process was enhanced when the pressure of the nitrogen plasmastep was set at 66.7 Pa than at 126.7 Pa.

The present invention is not limited to the embodiment described above,and it may be modified in various manners. For example, in theembodiment described above, the cleaning process is arranged to firstperform the oxygen plasma process, but it can be arranged to firstperform either the oxygen plasma process or nitrogen plasma process.Further, in the embodiment described above, the cleaning process isarranged to alternately supply O₂ gas and N₂ gas into the chamber 71 togenerate plasma. However, this is not limiting, and the cleaning processmay be differently applied as long as a gas containing oxygen and a gascontaining nitrogen are used. Examples of such gases are NO, NO₂, andNH₃.

The processing apparatus to be subjected to a process chamber cleaningmethod according to the present invention is exemplified by a processingapparatus of the low electron temperature plasma type, in whichmicrowaves are transmitted into a chamber through a planar antennahaving a plurality of slots to generate plasma. In this respect,microwaves may be transmitted through an antenna of anther type, or maybe transmitted into a process chamber without an antenna. In general,low electron temperature plasma is generated by used of microwaves.However, even where RF plasma of the inductive coupling type orparallel-plate type is used, low electron temperature plasma can begenerated by supplying pulsed RF. Accordingly, plasma of another typemay be used, as long as the plasma is applicable to a process chambercleaning process according to the present invention. Similarly, it isalso possible to use RF plasma of the magnetron type proposed in recentyears to generate low electron temperature plasma. Further, in theembodiment described above, as a typical example, the plasma source of aprocessing apparatus is used to perform a cleaning process. However, aprocessing apparatus may be provided with a plasma source for a cleaningprocess, other than a plasma source for a substrate process. In thiscase, the substrate processing apparatus may be arranged to perform anon-plasma process.

The invention claimed is:
 1. A substrate processing apparatus fornitriding or oxidizing a target substrate, the apparatus comprising: aprocess chamber configured to accommodate the target substrate; a gassupply mechanism configured to supply process gases into the processchamber; a plasma generation mechanism configured to turn gas intoplasma within the process chamber; and a control mechanism configured tocontrol an operation of the substrate processing apparatus, wherein thecontrol mechanism includes a computer readable non-transitory storagemedium storing a control program, which, when executed, causes thecontrol mechanism to control the apparatus to conduct a runningsequence, the running sequence comprising performing a cleaning cycle aplurality of times to remove metal contaminants within the processchamber in which the target substrate is not present, before performinga predetermined process for nitriding or oxidizing the target substrateplaced within the process chamber, the cleaning cycle including, in analternating manner, a first period of cleaning the process chamber bysupplying only a first mixture gas consisting of oxygen gas and argongas into the process chamber and generating first plasma of the firstmixture gas, and a second period of cleaning the process chamber bysupplying only a second mixture gas consisting of nitrogen gas and argongas into the process chamber and generating second plasma of the secondmixture gas, and wherein the running sequence comprises no period ofcleaning the process chamber by use of a fluorine-containing compoundinside the cleaning cycle or between the cleaning cycle and thepredetermined process.
 2. The apparatus according to claim 1, whereinthe plasma generation mechanism includes a planar antenna having aplurality of slots and disposed on the process chamber to face thetarget substrate, and each of the first plasma and the second plasma isgenerated by microwaves supplied into the process chamber through theplanar antenna.
 3. The apparatus according to claim 1, wherein therunning sequence further comprises performing either of a first processsequence and a second process sequence after said performing a cleaningcycle a plurality of times, and said either of the first processsequence and the second process sequence includes seasoning the processchamber in which the target substrate is not present by supplying aseasoning gas into the process chamber and generating plasma of theseasoning gas, and then performing the predetermined process on thetarget substrate placed within the process chamber by supplying aprocess gas into the process chamber and generating plasma of theprocess gas, such that the first process sequence uses the first mixturegas as the seasoning gas and uses a mixture gas consisting of oxygen gasand argon gas as the process gas to perform an oxidizing process as thepredetermined process, and the second process sequence uses the secondmixture gas as the seasoning gas and uses a mixture gas consisting ofnitrogen gas and argon gas as the process gas to perform a nitridingprocess as the predetermined process.
 4. The apparatus according toclaim 3, wherein the process chamber is provided with a table disposedtherein for placing the target substrate, and the cleaning cycle and theseasoning are performed while a dummy substrate is placed on the tableto protect the table.
 5. The apparatus according to claim 3, wherein theseasoning has a plasma generation time longer than either of the firstperiod and the second period of the cleaning cycle.
 6. The apparatusaccording to claim 1, wherein each of the first plasma and the secondplasma has an electron temperature of 2 eV or less.
 7. The apparatusaccording to claim 1, wherein the cleaning cycle includes supplyingargon gas into the process chamber without generating plasma of argongas and without supplying either of oxygen gas and nitrogen gas into theprocess chamber between the first period and the second period.
 8. Theapparatus according to claim 1, wherein the first mixture gas is setsuch that the oxygen gas is supplied at a flow rate smaller than that ofthe argon gas thereof and the second mixture gas is set such that thenitrogen gas is supplied at a flow rate smaller than that of the argongas thereof.
 9. The apparatus according to claim 1, wherein the runningsequence repeats the cleaning cycle to cause each of the metalcontaminants within the process chamber to be decreased to 2×10¹⁰atoms/cm² or less.
 10. A substrate processing apparatus for nitriding atarget substrate, the apparatus comprising: a process chamber configuredto accommodate the target substrate; a gas supply mechanism configuredto supply process gases into the process chamber; a plasma generationmechanism configured to turn gas into plasma within the process chamber;and a control mechanism configured to control an operation of thesubstrate processing apparatus, wherein the control mechanism includes acomputer readable non-transitory storage medium storing a controlprogram, which, when executed, causes the control mechanism to controlthe apparatus to conduct a running sequence, the running sequencecomprising performing a cleaning cycle a plurality of times to removemetal contaminants within the process chamber in which the targetsubstrate is not present, wherein the cleaning cycle includes, in analternating manner, a first period of cleaning the process chamber bysupplying only a first mixture gas consisting of oxygen gas and argongas into the process chamber and generating first plasma of the firstmixture gas, and a second period of cleaning the process chamber bysupplying only a second mixture gas consisting of nitrogen gas and argongas into the process chamber and generating second plasma of the secondmixture gas, then seasoning the process chamber in which the targetsubstrate is not present by supplying only the second mixture gas intothe process chamber and generating plasma of the second mixture gas, andthen performing a nitriding process on the target substrate placedwithin the process chamber, wherein the running sequence comprises noperiod of cleaning the process chamber by use of a fluorine-containingcompound inside the cleaning cycle or between the cleaning cycle and thenitriding process.
 11. The apparatus according claim 10, wherein theplasma generation mechanism includes a planar antenna having a pluralityof slots and disposed on the process chamber to face the targetsubstrate, and each of the first plasma and the second plasma isgenerated by microwaves supplied into the process chamber through theplanar antenna.
 12. The apparatus according to claim 10, wherein theprocess chamber is provided with a table disposed therein for placingthe target substrate, and the cleaning cycle and the seasoning areperformed while a dummy substrate is placed on the table to protect thetable.
 13. The apparatus according to claim 10, wherein each of thefirst plasma and the second plasma has an electron temperature of 2 eVor less.
 14. The apparatus according to claim 10, wherein the seasoninghas a plasma generation time longer than either of the first period andthe second period of the cleaning cycle.
 15. The apparatus according toclaim 10, wherein the cleaning cycle includes supplying argon gas intothe process chamber without generating plasma of argon gas and withoutsupplying either of oxygen gas and nitrogen gas into the process chamberbetween the first period and the second period.
 16. The apparatusaccording to claim 10, wherein the first mixture gas is set such thatthe oxygen gas is supplied at a flow rate smaller than that of the argongas thereof and the second mixture gas is set such that the nitrogen gasis supplied at a flow rate smaller than that of the argon gas thereof.17. The apparatus according to claim 10, wherein the running sequencerepeats the cleaning cycle to cause each of the metal contaminantswithin the process chamber to be decreased to 2×10¹⁰ atoms/cm² or less.18. The apparatus according to claim 10, wherein the nitriding processis performed by supplying as a process gas a mixture gas consisting ofnitrogen gas and argon gas into the process chamber and generatingplasma of the process gas.